The practice of applying lubricating coatings to magnet wire, which then aids in inserting the resulting electrical coils into their respective housings, is well documented (note commonly assigned U.S. Pat. Nos. 4,385,435; 4,385,436; 4,385,437; 4,545,323 and 4,601,918 the disclosure of which are herein incorporated by reference). The application of such coatings has taken many forms but one form which has proven successful is the use of a wicking felt applicator which is in contact with both the lubricating solution and the magnet wire substrate to be coated. The lubricating solution is drawn into the felt applicator and wicked through the porous body of the applicator to a surface which is in contact with the wire. As the wire passes across and in contact with the surface of the applicator, the lubricating solution is transferred from the applicator surface to the wire. To form a uniform concentric coating, the wire may be drawn between two applicators surrounding the wire, thereby ensuring uniformity of thickness and concentricity. After the wire has been coated, the solvent used to carry the lubricant solids is evaporated, leaving a lubricating layer about the exterior of the magnet wire.
As disclosed in the referenced patents above, these lubricating solutions are typically very low in solids content. Additionally, they are in a solution of highly volatile aliphatic hydrocarbon solvents such as naphtha, heptane and hexane or mixtures of same.
A problem develops during the application of these lubricants onto the wire, which results in a buildup of the lubricant on the exposed surface of the applicator. This results in uneven distribution and application of the lubricant onto the wire substrate, overtime, and difficulty in controlling the amount of lubricant being applied to the wire. In certain applications where such lubricated wire is used (i.e. hermetically sealed refrigeration compressors, etc.) the amount of lubricant applied per pound of wire must be tightly controlled to prevent the lubricant (which may be removed by the solvent within the system) from clogging the filters or other sensitive components (capillaries) of the unit and thereby preventing it from working properly. The amount of lubricant to be placed on the wire is specified by the manufacturer and is defined as the cleanliness number. This number is defined as the amount of lubricant by weight placed on a specified weight of wire. Typical units used to specify such a requirement is milligrams of lubricant per pound of wire (mgm/lb). These specifications are most often described in terms of maximum quantities of lubricant as too much lubricant is more harmful to the system than too little. Oftentimes these cleanliness numbers are difficult to attain due to the nonuniform application of the lubricant.
Additionally it has been found that the applicator often contains residual lubricant particles, which are now in a highly viscous, high solids condition. As the wire passes in contact with the applicator, this material will periodically be transferred from the applicator to the wire, again forming a nonuniform application of the lubricant and increasing the cleanliness number of the resulting wire.
Therefore, what is required in the art is a felt applicator which permits more uniform application of the lubricant to the wire, both in distribution and quantity, thereby producing a wire with lower and more consistent cleanliness numbers.